On Making Diesel from Coal Pt. 1

On Making Diesel from Coal Pt. 1

I had a colloquy with a friend from The Wilderness Society about building plants to convert coal to liquid fuels, such as gasoline and diesel. He, a former Montanan living in D.C., had read about Montana’s Governor Schweitzer wanting to promote conversion of coal to diesel, and he was not happy.

Having studied organic chemistry, power generation and coal, I offered this analysis: (Reader alert: this is a three-part primer in carbon-based chemistry, mixed with a bit of economics and a dash of social policy. There will not be an exam, unless the acclamations of readers demand one.)

It’s all just oxidation and reduction.

Hydrocarbons contain carbon to hydrogen bonds and carbon to carbon bonds. Breaking these bonds and attaching oxygen to the carbon and hydrogen atoms is what generates heat, therefore energy; capturing this energy can move pistons or turbines. Carbon plus oxygen is usually CO2. sometimes in an oxygen starved environment like a mobile home, CO (carbon monoxide).

In your body, you eat carbohydrates, complexes of carbon and hydrogen, which are oxidized in your body, i.e ., combined with oxygen, and you exhale the carbon dioxide. You are a mini-power-plant. But if you fart, other gases enter the atmosphere, so you are not a totally clean mini-power-plant, either.

A coal power plant oxidizes the carbon (yielding CO2), the hydrogen (yielding water), and some of the impurities in the coal (yielding SO2 and other substances). NO2 and other nitrogen oxides come from the air; nitrogen in the atmosphere is incidentally oxidized in the combustion chamber, helping to create smog.

Your plump or lithe body does the same thing, on a smaller scale. The more you exercise, the more CO2 you put into the atmosphere.

A modern coal power plant uses electrostatic precipitators to capture solids (fly ash) and limestone-loaded scrubbers to capture SO2 and other contaminants (including part of the mercury, which does not oxidize; that is elemental mercury does not combine with oxygen). These devices consume up to 20-25 percent of the gross power output of the steam generators. That means that we burn more coal to generate the power to drive the pollution controls. That means we release more CO2 to control the SO2, etc.